In a storage system including plural storage devices, such as a RAID (Redundant Array of Inexpensive Disks) composed of plural magnetic disks, technologies of rapidly restoring system failures are proposed. For example, Japanese Laid-Open Patent Application Publication No. 2007-316879 discloses a technology for significantly reducing automatic restoration time to restore a loop of the loop-connected storage devices. In this example, when loop abnormality is detected in the loop-connected storage devices, the loop-connected storage devices are diagnosed in parallel. Thus, automatic restoration of the loop may be implemented in a short time.
Similarly, Japanese Laid-Open Patent Application Publication No. 2007-141185 discloses a technology for detecting a failure of disk drives in an early stage, so that usability of the drives may be immediately restored. In this example, when an error is detected in a switching circuit that is connected between the disk drives and a low order communication controller, the detected error is reported from an error monitor to the low order communication controller. Accordingly, the restoration of the disk drive failure may be immediately initiated.
Further, Japanese Laid-Open Patent Application Publication No. 2006-285519 discloses a technology for quickly specifying a failure of a data transfer system. In this example, an upstream device transmits diagnostic data failure to a downstream device and also to the upstream device itself, so that the normality of the transmitted diagnostic data may be evaluated. If the downstream device abnormally receives the diagnostic data transmitted from the upstream device, an interval between the upstream device and the downstream device is specified as a failed interval. The upstream device subsequently receives the diagnostic data transmitted by its own receiver to carry out return diagnosis, thereby further specifying location of the failure.